Process For The Preparation Of Zeolites Having CHA Structure

ABSTRACT

The present invention relates to a process for the preparation of zeolites having CHA framework structure and a composition comprising the molar ratio (n SiO 2 ):X2O 3 , wherein X is a trivalent element, and wherein n is at least 10, the process comprising (i) preparation of an aqueous solution containing at least one source for X 2 O 3 , wherein X is selected from Al, B, Ga, and a mixture of two or more, and at least one source for SiO 2 , at least one organic structure directing agent (SDA) other than Tetrame-thylammonium hydroxide (TMAOH), acting as a template for the CHA structure, and Tetramethylammonium hydroxide (TMAOH), wherein the SDA or mixtures thereof are employed in such amounts that the aqueous solution in (i) exhibits a molar ratio of SDA:TMAOH of 0.01 to 5; (ii) hydrothermal crystallization of the aqueous solution according to (i); wherein the aqueous solution of (i) contains copper in an amount less than 0.005 Cu:((n YO 2 )+X 2 O 3 ) where n is in the range of 10 to 50. The present invention also relates to the zeolitic materials obtainable and/or obtained by this process as well as to a zeolitic material as such, having framework structure CHA, having a composition comprising the molar ratio (n SiO 2 ):X 2 O 3 , wherein X is a trivalent element and n is at least 10, and wherein the crystal size, as determined from Scanning Electron Microscopy, is greater than 1 micrometer and wherein the chabazite framework is phase-pure having an impurity of other zeolitic frameworks, such as RUT as determined by X-ray Diffraction, of less than 5%.

The present invention relates to a process for the preparation ofzeolites having CHA framework structure and a composition comprising themolar ratio (n SiO₂):X₂O₃, wherein X is a trivalent element, and whereinn is at least 10, the process comprising

-   -   (i) preparation of an aqueous solution containing at least one        source for X₂O₃, wherein X is selected from Al, B, Ga, and a        mixture of two or more, and at least one source for SiO₂, at        least one organic structure directing agent (SDA) other than        Tetramethylammonium hydroxide (TMAOH), acting as a template for        the CHA structure, and Tetramethylammonium hydroxide (TMAOH),        wherein the SDA or mixtures thereof are employed in such amounts        that the aqueous solution in (i) exhibits a molar ratio of        SDA:TMAOH of 0.01 to 5;    -   (ii) hydrothermal crystallization of the aqueous solution        according to (i);        wherein the aqueous solution of (i) contains copper in an amount        less than 0.005 Cu:((n SiO₂)+X₂O₃) where n is at least 10.

The present invention also relates to the zeolitic materials obtainableand/or obtained by this process as well as to a zeolitic material assuch, having framework structure CHA, having a composition comprisingthe molar ratio (n SiO₂):X₂O₃, wherein X is a trivalent element and n isat least 10, and wherein the crystal size, as determined from ScanningElectron Microscopy, is greater than 1 micrometer and wherein thechabazite framework is phase-pure having an impurity of other zeoliticframeworks, such as RUT as determined by X-ray Diffraction, of less than5%, based on the total zeolitic framework.

Zeolitic materials having chabazite (CHA) framework structure are widelyused in important actual technical areas such as in the automotiveindustry where the materials are employed as catalysts. The reduction ofnitrogen oxides with ammonia to form nitrogen and H₂O can be catalyzedby metal-promoted zeolites to take place preferentially to the oxidationof ammonia by the oxygen or to the formation of undesirable sideproducts such as N₂O, hence the process is often referred to as the“selective” catalytic reduction (“SCR”) of nitrogen oxides, and issometimes referred to herein simply as the “SCR” process. The catalystsemployed in the SCR process ideally should be able to retain goodcatalytic activity over the wide range of temperature conditions of use,for example, 200° C. to 600° C. or higher, under hydrothermal conditionsand in the presence of sulfur compounds. High temperature andhydrothermal conditions are often encountered in practice, such asduring the regeneration of the catalyzed soot filter, a componentnecessary for the aftertreatment of exhaust off-gas. Thus, thesematerials are of high economical and ecological interest. Due to thesaid technical areas and the resulting need of high amounts of thematerials, there is an increasing demand for efficient processes for thepreparation of these materials.

Molecular sieves are classified by the Structure Commission of theInternational Zeolite Association according to the rules of the IUPACCommission on Zeolite Nomenclature. According to this classification,framework-type zeolites and other crystalline microporous molecularsieves, for which a structure has been established, are assigned a threeletter code and are described in the Atlas of Zeolite Framework Types,5th edition, Elsevier, London, England (2001). Chabazite is one of themolecular sieves for which a structure has been established, and thematerial of this framework-type is designated as CHA. Zeolitic materialsas used herein are defined as metallosilicate frameworks includingaluminosilicates, borosilicates and gallosilicates. It does not includethe MeAPSO, APSO, or AIPO family of materials.

Chabazite is a zeolite which occurs in nature and also has syntheticforms. Synthetic forms are described in “Zeolite Molecular Sieves” byBreck (1973). The structure of Chabazite is described in “Atlas ofZeolite Structure Types” by Meier and Olson (1978). The Chabazitestructure has been designated with the structure code, “CHA”.

Natural Chabazite exists in nature and has a SiO₂:Al₂O₃ typically lessthan 10. Synthetic forms of this low SiO₂:Al₂O₃ range include zeolite“K-G”, zeolite D and zeolite R. Zeolite “K-G” is reported by Barrer etal. in J. Chem. Soc., 1956, p 2892-. Zeolite D is reported in Britishpatent number 868,846. Zeolite R is reported in U.S. Pat. No. 3,030,181.

Synthesis of high-silica Chabazite (>10 SiO₂:Al₂O₃) is reported in U.S.Pat. No. 4,544,538, U.S. Pat. No. 6,709,644 and US 2003/0176751 A1.

U.S. Pat. No. 6,709,644 discloses a high-silica CuChabazite (SSZ-62)with small crystal size (<0.5 microns) with application in SCR of NOx.

WO 2008/106519 discloses a catalyst comprising: a zeolite having the CHAcrystal structure and a mole ratio of silica to alumina greater than 15and an atomic ratio of copper to aluminum exceeding 0.25. The catalystis prepared via copper exchanging NH₄ ⁺-form CHA with copper sulfate orcopper acetate. Catalytic activity is largely retained afterhydrothermal aging at 850° C. for 6 hours.

WO 2008/132452 discloses a number of zeolite materials, includingCuSSZ-13, that can be loaded with iron and/or copper. Catalytic activityis largely retained after hydrothermal aging of CuSSZ-13 at 900° C. for1 hour. Although no specific mention of Na levels appears it is statedthan an ammonium exchange is employed prior to the Cu exchange to removeNa.

WO 2008/118434 indicates that a CuSSZ-13 (15 to 60 SiO₂:Al₂O₃) materialthat can retain at least 80% of its surface area and micropore volumeafter hydrothermal aging at 900° C. in 10% steam for 1 to 16 hours wouldbe suitable for application in SCR. Example 3 indicates that an ammoniumexchange is carried out to remove residual Na. Additionally, acomparison of medium-sized crystals to large-sized crystals of SAPO-34indicated improved stability for the larger crystals.

In all cases Na is first removed by ammonium exchange prior to theintroduction of Cu. The resultant Na content is not disclosed. In table8 of U.S. Pat. No. 4,544,538 Na contents of >0.5% Na₂O are reported forexamples 2 through 5 following ammonium exchange. Prior to ammoniumexchange the Chabazites prepared with alkali metal hydroxides in thesynthesis gel would be expected to contain >0.5 wt % Na₂O.

The state of the art preparation of a Cu-Chabazite is described by thefollowing key steps:

-   -   1. Crystallization of a alkali metal/SDA containing chabazite        and separation from the synthesis gel    -   2. Drying and calcination to remove the SDA leading to the        H—Na(alkali) form of Chabazite    -   3. Ammonium exchange to remove alkali metals    -   4. Copper exchange to introduce Cu

This invention discloses an improved process:

-   -   1. Crystallization of TMA/SDA containing chabazite and        separation from the synthesis gel    -   2. Drying and calcination to remove the SDA leading to the        H-form of Chabazite    -   3. Copper exchange to introducte Cu

Removal of alkali metals is important for the stability and activity ofSCR catalysts. WO 2008/132452 suggests that the poor SCR performance ofan alkali-metal containing CuChabazite could be attributed to poisoningof the acid sites and report little activity even in the fresh catalyst.Whereas, U.S. application Ser. No. 12/612,142 filed on Nov. 4, 2009indicates good SCR performance of a Cu-Chabazite prepared from a similarparent material where the alkali-metals have been largely removedsupporting the importance of low alkali-metal content.

Many catalytic uses for zeolitic materials involve the H-form and sostep 2 of the inventive process already delivers an active materialwithout the need for further processing. Such an application couldinclude catalysts used in methanol to olefin chemistry.

Furthermore, the ion-exchange steps can lead todealumination/deboronation due to the acidic pH conditions employed. Thedealumination/deboronation limits the amount of active cations that canbe introduced since it results in loss of exchange capacity and can leadto instability of the zeolite structure. Dealumination is linked toinstability of SCR catalysts such as CuZSM-5 (Journal of Catalysis,1996, p 43-).

Thus, the disadvantage of the multi-step synthesis route is thedealumination which can occur during ion-exchange steps. Additionally,each exchange step adds additional cost and additional complexity to theprocess. Partial replacement of expensive template molecules, such astrimethyladamantyl ammonium hydroxide, with tetramethylammoniumhydroxide offers additional cost savings. The invention process resultsin a lower cost, less complex and less damanging synthesis route for theproduction of H-Chabazite and other metal containing forms of Chabazite.

Tetramethylammonium hydroxide (TMAOH) has been utilized as a templatingagent and OH⁻ source in numerous zeolite, zeolitic (e.g. borosilicate,gallosilicate etc) and non-zeolitic (i.e. AIPO, MeAPO, and MeAPSOcompositions) syntheses including the preparation of ATT, CAN, CHA, EAB,ERI, ERI/OFF, FAU, FER, GIS, GME, LTA, MAZ, OFF, and SOD.

Barrer et al. discusses the role of OH⁻ as a mineralizing agent togetherwith the structure directing role of cations such as alkali metals andorganic additives or templates (Zeolites, 1981, p 130). Control of bothis critical for the selective crystallization of zeolite phases.

A number of Aluminophosphate materials can be crystallized using TMAOHincluding AIPO-12 (ATT—J. Phys. Chem., 1986, p 6122), AIPO-33 (ATT—U.S.Pat. No. 4,473,663), ZnAPSO-43 (GIS—EP 158,975), ALPO-20 (SOD—U.S. Pat.No. 4,310,440), BeAPSO-20 (SOD—U.S. Pat. No. 4,737,353), MgAPSO-20(SOD—EP 158,348), MnAPSO-20 (SOD—EP 161,490) and ZnAPSO-20 (SOD—EP158,975). These systems are synthesized in the absence of an alkalimetal hydroxide since these materials typically crystallize in nearneutral pH or less alkaline pH than the aluminosilicates materials.Consequently, these materials are considered alkali-metal free.Tetramethylammonium (TMA) is occluded within the microporous cavities ofthe material during crystallization.

The synthesis of the aluminosilicates ERI and OFF are described in manyarticles due to the overlapping synthesis conditions that often resultin the intergrown product of the two known as ZSM-34. This complexity iscomprehensively described in Zeolites, 1986, p 745. In all cases alkalimetal hydroxides are used in combination with TMA. This paper representsthe structures of ERI and OFF with the TMA cation occluded within thecages. The independent phases can be prepared by careful control of gelcomposition. Barrer et al. described the combination of TMA with alkalimetal hydroxides for the preparation of CAN, LTA, OFF, ERI, EAB, GME,SOD and MAZ (Zeolites, 1981, p 130). The aluminosilciate, EABcrystallizes from a Na or K and TMA gel at temperatures of about 80° C.(J. Solid State Chem., 1981, p 204). In all cases the syntheses report acombination of TMA with an alkali metal resulting in the incorporationof both in the zeolite product.

Chabazite (zeolite ZK-14) with low SiO₂:Al₂O₃ has also been reported toform with (K, Na, TMA) mixtures where K is preferred (Molec. Sieves,Soc. Chem. Ind., 1968, p 85). U.S. Pat. No. 4,544,538 teaches thesynthesis of high silica chabazite from trimethyladamantylammoniumhydroxide (TMAA) and sodium hydroxide reaction gels. It is mentionedthat sodium hydroxide could be replaced by the addition of moretemplate, whereas the template is typically a bicycle hetereoatomcompound. It is disclosed that the preferred OH/Si ratio is <0.96 forthe formation of chabazite with >20 SiO₂:Al₂O₃. However, the addition ofmore template would result in a significant increase in cost and perhapsissues with waste water due to increased residual organic in the motherliquor following crystallization.

Zeolite RUT (Nu-1—U.S. Pat. No. 4,060,590 and RUB10, Z. Kristallogr.,1995, p 475) is formed from gels containing TMAOH with crystallizationtemperatures of 150 to 200° C. and reaction times of about 1.5 to 3days. This is a common impurity phase when TMAOH is used as areplacement for alkali metal hydroxides in Chabazite synthesis due tosimilar reaction conditions. Increased amounts of TMAOH lead to RUTbecoming the majority phase.

U.S. Pat. No. 3,306,922 describes a synthesis of zeolites N-X and N-Y(FAU), N-B and N-A (LTA) containing a substantial weight percent of acation other than sodium or other metal cation. Specifically a low Naproduct is attained by using TMAOH as the only source of OH⁻ andstructure direction.

The prior art indicates that use of TMAOH, as the only organic sourceand in the absence of alkali-metals, would result in zeolites RUT, N-X,N-Y. N-B or N-A. No reports exist of Chabazite formation in the presenceof only TMAOH.

Therefore, it is an object of the present invention to provide a timeand cost saving process for the preparation of zeolitic materials havingCHA framework structure.

It is a further object of the present invention to provide a novelprocess for the preparation of zeolitic materials having CHA frameworkstructure resulting in essentially phase-pure chabazite avoidingimpurities such as zeolite RUT.

It is a further object of the present invention to provide a novelprocess for the preparation of containing zeolitic materials having CHAframework structure, wherein the zeolitic material has crystal sizegreater than about 1 micron.

It is a further object of the present invention to provide a novelprocess for the preparation of zeolitic materials having CHA frameworkstructure resulting in essentially alkali-free and/or earth alkali-freechabazite.

It is a further object of the present invention to provide a novelprocess for the preparation of containing zeolitic materials having CHAframework structure, wherein the zeolitic material contains Si and Al ina high molar ratio of Si:Al.

Therefore, the present invention relates to a process for thepreparation of zeolites having CHA framework structure and a compositioncomprising the molar ratio (n SiO₂):X₂O₃, wherein X is a trivalentelement, and wherein n is at least 10, the process comprising

-   (i) preparation of an aqueous solution containing at least one    source for X₂O₃, wherein X is selected from Al, B, Ga, and a mixture    of two or more, and at least one source for SiO₂, at least one    organic structure directing agent (SDA) other than    Tetramethylammonium hydroxide (TMAOH), acting as a template for the    CHA structure, and Tetramethylammonium hydroxide (TMAOH), wherein    the SDA or mixtures thereof are employed in such amounts that the    aqueous solution in (i) preferably exhibits a molar ratio of    SDA:TMAOH of about 0.01 to about 5,-   (ii) hydrothermal crystallization of the aqueous solution according    to (i);    wherein the aqueous solution of (i) contains copper in an amount    less than 0.005 Cu: ((n SiO₂)+X₂O₃) where n is at least 10.

This invention is a cost efficient synthesis route to essentiallyalkali/earth alkali metal free chabazite by utilizing TMAOH as areplacement for alkali/earth alkali metal hydroxyides (e.g. NaOH orKOH). The synthesis results in essentially phase-pure chabazite avoidingimpurities such as zeolite RUT. Additionally, the product has crystalsize greater than about 1 micron.

As used in this specification and the appended claims, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly indicates otherwise. Thus, for example, reference to “acatalyst” includes a mixture of two or more catalysts, and the like.

Preferably the Chabazite molecular sieve includes all aluminosilicate,borosilicate, and gallosilicate compostions. These include, but are notlimited to SSZ-13, SSZ-62, natural chabazite, zeolite K-G, Linde D,Linde R, LZ-218, LZ-235. LZ-236, and ZK-14. Most preferrably thematerial will have the aluminosilicate composition, such as SSZ-13 andSSZ-62.

According to stage (i) of the present invention, all conceivable sourcesfor trivalent elements X may be employed which can build up the zeoliticframework and which, as part of this zeolitic framework, are referred toas X₂O₃ in the context of the present invention.

Preferably, the trivalent element X is selected from the groupconsisting of Al, B, Ga, and a mixture of two or more thereof.

Generally, all suitable sources for B₂O₃ can be employed. By way ofexample, borates and/or boric acid, metaboric acid, ammonium metaborate,and/or boric acid esters such as boric acid triethyl ester or boric acidtrimethyl ester may be mentioned. Generally, all suitable sources forGa₂O₃ can be employed. By way of example, Ga nitrates may be mentioned.

Generally, all suitable sources for Al₂O₃ can be employed, however, aAl₂O₃ source is preferably employed which is free of alkali and/or earthalkali metal, in particular free of sodium. By way of example, metallicaluminum such as aluminum powder, suitable aluminates such as alkalimetal aluminates, aluminum alcoholates such as aluminumtriisopropylateand aluminum hydroxide may be mentioned. According to a preferredembodiment of the present invention, however, an Al₂O₃ source isemployed which is free of alkali and/or earth alkali metal, inparticular free of sodium. Aluminum hydroxide, Al(OH)₃, andaluminumtriisopropylate are especially preferred.

According to an especially preferred embodiment of the presentinvention, the trivalent element X is Al, and even more preferably, noother trivalent element is used, Al thus being the only trivalentelement building up the CHA zeolitic framework structure.

Generally, all suitable sources for SiO₂ can be employed, however, aSiO₂ source is preferably employed which is free of alkali and/or earthalkali metal, in particular free of sodium. By way of example,silicates, silica, silicic acid, colloidal silica, fumed silica,tetraalkoxysilanes, silica hydroxides, precipitated silica or clays maybe mentioned. In this context, both so-called “wet-process silicondioxide” as well as so called “dry-process silicon dioxide” can beemployed. Colloidal silicon dioxide is, inter alia, commerciallyavailable as Ludox®, Syton®, Nalco®, or Snowtex®. “Wet process” silicondioxide is, inter alia, commercially available as Hi-Sil®, Ultrasil®,Vulcasil®, Santocel®, Valron-Estersil®, Tokusil® or Nipsil®. “Dryprocess” silicon dioxide is commercially available, inter alia, asAerosil®, Reolosil®, Cab-O-Sil®, Fransil® or ArcSilica®.Tetraalkoxysilanes, such as, for example, tetraethoxysilane ortetrapropoxysilane, may be mentioned.

According to preferred embodiments of the present invention, dry-processsilica or colloidal silica is employed. If colloidal silica is employed,it is further preferred that said colloidal silica is stabilized withoutalkali and/or earth alkali metal, in particular without sodium.According to even more preferred embodiments where colloidal silica isused, the colloidal silica employed as aqueous solution in (i) isstabilized with ammonia.

Generally, the sources for X₂O₃ and SiO₂ can be employed in allconceivable amounts and molar ratios for the preparation of the aqueoussolution in (i) with the proviso that in (ii), a zeolite having CHAframework structure is obtained.

According to a preferred embodiment of the present invention, the atleast one source for SiO₂ and the at least one source for X₂O₃ areemployed in such amounts that the aqueous solution obtained according to(i) exhibits a molar ratio

(nSiO₂):X₂O₃

wherein n is at least 10, more preferably at least 15. More preferably,n is in the range of from 15 to 80, more preferably from 15 to 60, morepreferably from 15 to 50 such as, e.g., 15, 20, 25, 30, 35, 40, 45, 50.

As far as the structure directing agent employed in (i) is concerned, norestriction exists with the proviso that a zeolitic material having CHAframework structure is obtained in (ii).

By way of example, a suitable N-alkyl-3-quinuclidinol, a suitableN,N,N-trialkylexoaminonorbornane, a suitableN,N,N-trimethyl-1-adamantylammonium compound, a suitableN,N,N-trimethyl-2-adamantylammonium compound, a suitableN,N,N-trimethylcyclohexylammonium compound, a suitableN,N-dimethyl-3,3-dimethylpiperidinium compound, a suitableN,N-methylethyl-3,3-dimethylpiperidinium compound, a suitableN,N-dimethyl-2-methylpiperidinium compound,1,3,3,6,6-pentamethyl-6-azonio-bicyclo(3.2.1)octane,N,N-dimethylcyclohexylamine, or a suitable N,N,N-trimethylbenzylammoniumcompound may be mentioned. As suitable compounds, the hydroxides ofabove-mentioned compounds may be mentioned. PreferablyN,N,N-trimethyl-1-adamantylammonium hydroxide is employed as SDA.

Preferably, a suitable N,N,N-trimethyl-1-adamantylammonium(1-adamantyltrimethyl ammonium) compound is employed. Optionally, thissuitable 1-adamantyltrimethylammonium compound can be employed incombination with at least one further ammonium compound such as, e.g., aN,N,N-trimethylbenzylammonium (benzyltrimethylammonium) compound or atetramethylammonium compound or a mixture of a benzyltrimethylammoniumand a tetramethylammonium compound.

As far as the ammonium compounds are concerned, it is conceivable that asuitable salt of the ammonium compounds is employed. Preferably, if suchsalt is employed, this salt or the mixture of salts should impart thedesired pH to the aqueous solution to be subjected to hydrothermalcrystallization. If necessary, a suitable base such as, for example, asuitable hydroxide source, can be added, in addition said salt(s) toimpart said pH. Preferably, according to the present invention, theammonium salt or ammonium salts as such are the suitable base,preferably the hydroxide source, i.e., it is preferred that the ammoniumcompound(s) is/are employed as hydroxide(s).

As far as the ammonium compounds are concerned, it is also possibleaccording to the present invention to employ the respective aminecompound, if necessary in combination with at least one suitable basesuch as, e.g. a suitable hydroxide source

Generally, the sources for X₂O₃ and SiO₂ and the structure directingagent can be employed in all conceivable amounts and molar ratios forthe preparation of the aqueous solution in (i) with the proviso that in(ii), a zeolite having CHA framework structure is obtained.

According to a preferred embodiment of the present invention, the atleast one source for SiO₂ and the at least one source for X₂O₃ areemployed in such amounts that the aqueous solution obtained according to(i) exhibits a molar ratio of structure directing agent (SDA),optionally the sum of SDAs, relative to the sum of (n X₂O₃) and SiO₂,

(pSDA):((nSiO₂)+X₂O₃)

wherein p is at least 0.035, more preferably at least 0.07, morepreferably at least 0.15. Even more preferably, p is less than or equalto 0.6, more preferably less than or equal to 0.5, more preferably lessthan or equal to 0.4, more preferably less than or equal to 0.3, andmore preferably less than or equal to 0.2. Thus, according to preferredembodiments of the present invention, p is in the range of from 0.035 to0.6, more preferably from 0.07 to 0.4, and even more preferably from0.15 to 0.2.

Preferably, the pH of the aqueous solution obtained from (i) andsubjected to hydrothermal crystallization according to (ii) is at least10, more preferably at least 11, and even more preferably at least 12.More preferably, the pH of the aqueous solution subjected tohydrothermal crystallization according to (ii) is in the range of from10 to 14, even more preferred in the range from 12 to 14.

Thus, the present invention also relates above-described process,wherein the pH of the aqueous solution subjected to (ii) is in the rangeof from 12 to 14.

Tetramethylammonium hydroxide is used to adjust the pH and OH/Si of theaqueous solution subjected to hydrothermal crystallization according to(ii) so that the pH has above-described values, depending on thestarting materials employed.

According to a preferred embodiment of the present invention, thestructure directing agent (SDA) or mixtures thereof are employed in suchamounts that the aqueous solution obtained according to (i) exhibits amolar ratio of tetramethylammonium hydroxide (TMAOH) relative tostructure directing agent (SDA),

(rTMAOH):(SDA)

wherein r is preferably in the range of 0.1 to 5 preferred 0.7 to 5,even more preferred 0.7 to 4, even more preferred 0.7 to 3, even morepreferred 1.1 to 3, even more preferred 1.1 to 2, even more preferred1.1 to 1.6.

In addition to tetramethylammonium hydroxide a base which does notcontain alkali and/or earth alkali metal, preferably a base which doesnot contain sodium, can be used for adjusting the pH.

According to a preferred embodiment of the present invention, the OH⁻/Siratio in the aqueous solution obtained according to (i) is preferably inthe range of 0.1 to 1, more preferred in the range of 0.1 to 0.5, evenmore preferred in the range of 0.1 to 0.3, even more preferred in therange of 0.1 to 0.2, even more preferred in the range of 0.12 to lessthan 0.2.

As already described above, the at least one source for SiO₂ and the atleast one source for X₂O₃, preferably Al₂O₂, are free of alkali and/orearth alkali metals, in particular free of sodium. According to an evenmore preferred embodiment of the present invention, the aqueous solutionobtained in (i) and subjected to hydrothermal crystallization in (ii) isfree of alkali and/or earth alkali metals, in particular free of sodium.

The term “free of alkali metal” and “free of sodium”, as used in thiscontext of the present invention relates to the fact that no startingmaterials are employed which contain sodium, in particular alkali metalas essential component, such as, e.g., sodium aluminate as source forAl₂O₂, or the like. However, this term does not exclude such embodimentswhere the starting materials explicitly described contain certainamounts of sodium, in particular alkali metals as impurities. By way ofexample, such impurities are typically present in amounts of 1000 ppm orless, preferably 500 ppm or less, more preferably 300 ppm or less. Theterm “an alkali metal content of X ppm or less” as used in the contextof the present, relates to an embodiment according to which the sum ofall alkali metals present does not exceed X ppm. In all cases alkalimetal content is reported on the basis of its metal oxide e.g. 1000 ppmNa₂O. It is recognized that cationic Na⁺ resides within the zeolitepores.

Therefore, the present invention also relates to above-describedprocess, wherein the aqueous solution subjected to hydrothermalcrystallization according to (ii) is free of alkali and/or earth alkalimetals, in particular free of alkali metal.

According to further embodiments, the aqueous solution obtainedaccording to (i) may contain further metals, such as, for example, Ti,transition metals, such as Fe, Mo and/or Co, and/or lanthanides, such asLa, Ce, Y.

More preferred the aqueous solution obtained according to (i) containscopper in an amount less than 0.5 wt %, preferable less than 0.1 wt %.Even more preferred the aqueous solution obtained according to (i) isfree of copper.

The term “free of copper” as used in this context of the presentinvention relates to the fact that no starting materials are employedwhich contain copper. However, this term does not exclude suchembodiments where the starting materials explicitly described containcertain amounts of copper as impurities. By way of example, suchimpurities are typically present in amounts of 1000 ppm or less,preferably 500 ppm or less, more preferably 100 ppm or less.

Generally, there are no specific restrictions in which order thestarting materials are mixed to obtain the aqueous solution according to(i).

According to one embodiment of the present invention, an aqueoussolution containing the at least one structure directing agent and TMAOHis optionally mixed with ammonia. In this solution, the at least onesource for X₂O₃, preferably Al₂O₃, and the at least one source for YO₂,preferably SiO₂, are suspended.

According to another embodiment of the present invention, an aqueoussolution containing the at least one source for X₂O₃, preferably Al₂O₃,is admixed with the at least structure directing agent and TMAOH,wherein, subsequently, the at least one source for YO₂, preferably SiO₂,is added.

According to a preferred embodiment of the present invention, the atleast one source for SiO₂ and the at least one source for X₂O₃ areemployed in such amounts that the aqueous solution obtained according to(i) exhibits a molar ratio of water relative to the sum of (n X₂O₃) andSiO₂, relative to the structure directing agent (SDA), optionally thesum of SDAs, and TMAOH

(qH₂O):[(nSiO₂)+X₂O₃]:(sSDA):(tTMAOH)

wherein q is preferably at least 10, more preferably at least 15 andeven more preferably at least 20,wherein n is preferably 5 to 1000, more preferred 5 to 100, even morepreferred 10 to 50;wherein s is preferably 0.025 to 0.1, more preferred 0.05 to 0.075, evenmore preferred 0.05 to 0.065;wherein t is preferably 0.01 to 0.1 more preferred 0.01 to 0.1, evenmore preferred 0.03 to 0.1.

Even more preferably, said q is less than or equal to 70, morepreferably less than or equal to 65, more preferably less than or equalto 60, more preferably less than or equal to 55, and more preferablyless than or equal to 50. Thus, according to preferred embodiments ofthe present invention, q is in the range of from 10 to 70, morepreferably from 15 to 60, and even more preferably from 20 to 50.

The temperature during the preparation of the aqueous solution accordingto (i) is preferably in the range of from 10 to 40° C., more preferablyin the range of from 15 to 35° C., and particularly preferably in therange of from 20 to 30° C.

In principle, it is possible to heat the aqueous solution according to(ii) under any suitable pressure and any suitable temperature ortemperatures, provided that it is ensured that zeolitic material of CHAframework structure crystallizes in the solution. Here, temperatureswhich, at the chosen pressure, are above the boiling point of thesolution obtained according to (i) are preferred. Temperatures of up to200° C. at atmospheric pressure are more preferred. The term“atmospheric pressure” as used in the context of the present inventiondesignates a pressure of, ideally, 101 325 Pa, which, however, may besubject to variations within the limits known to the person skilled inthe art.

According to a particularly preferred embodiment of the processaccording to the invention, the hydrothermal crystallization accordingto (ii) is carried out in an autoclave.

The temperature used in the autoclave according to (ii) is preferably inthe range of from 100 to 200° C., more preferably in the range of from130 to 19° C., more preferably in the range of from 140 to 180° C.

According to an even more preferred embodiment of the present invention,the autoclave employed for carrying out the hydrothermal crystallizationaccording to (ii) exhibits means for heating and cooling the content ofthe autoclave, more preferably external heating means such as a suitableheating/cooling jacket.

This temperature to which the aqueous solution is heated according to(ii) can in principle be maintained until the crystallization has takenplace to the desired extent. Here, time periods of up to 340 h, morepreferably from 1 h to 260 h, and more preferably from 8 to 110 h arepreferred. According to further preferred embodiments of the presentinvention, crystallization times are in the range of from 12 to 72 h,more preferably from 24 to 48 h.

During crystallization, pressure or pressures in the range of from 1 to20 bar, more preferably from 2 to 10 bar and even more preferably from 5to 8 bar are especially preferred.

The aqueous solution is preferably suitably stirred for thecrystallization according to (ii). It is also possible to rotate thereaction vessel in which the crystallization is carried out. Typicalvalues as far as said stirring or rotation is concerned are in the rangeof from 40 to 250 rpm such as from 50 to 250 rpm (revolutions perminute).

It is possible in the context of the present invention to add suitableseeding material to the solution subjected to stage (ii), such asoptionally dried and/or calcined zeolitic material having CHA frameworkstructure. Seeding may be advantageous, in particular with regard tocrystallinity of the obtained chabazite material and the hydrothermalcrystallization time. In the case where Al or Ga or mixtures thereof areused as X₂O₃, it is preferred to carry out the hydrothermalcrystallization and in particular the whole inventive process withoutseeding material.

After hydrothermal crystallization according to (ii), the mother liquorcontaining the inventive zeolitic material having CHA frameworkstructure is suitably separated from said mother liquor. Prior toseparation, the temperature of the mother liquor containing the zeoliticmaterial may be suitably decreased to a desired value employing asuitable cooling rate. Typical cooling rates are in the range of from 15to 45° C./h, preferably from 20 to 40° C./h, and even more preferablyfrom 25 to 35° C./h.

Typical temperatures of the cooled mother liquor containing theinventive zeolitic material having CHA framework structure are in therange of from 25 to 55° C., preferably of from 35 to 50° C.

According to one embodiment of the process according to the invention,the zeolitic material having CHA framework structure is separated in asuitable manner in at least one step from the suspension, i.e. themother liquor containing the zeolitic material, obtained from (ii). Thisseparation can be effected by all suitable methods known to the skilledperson, for example, by decantation, filtration, ultrafiltration,diafiltration or centrifugation methods or, for example, spray dryingand spray granulation methods.

Therefore, the present invention also relates to above-describedprocess, additionally comprising

(iii) separating the zeolitic material from the suspension obtainedaccording to (ii).

If, e.g., the zeolitic material is separated by filtration orcentrifugation or concentration of the suspension obtained according to(ii), it is preferred that that the separated zeolitic material issuitably dried. Before the separated zeolitic material is dried, it maybe washed at least once with a suitable washing agent, wherein it ispossible to use identical or different washing agents or mixtures ofwashing agents in the case of at least two of the washing steps and touse identical or different drying temperatures in the case of at leasttwo drying steps.

Washing agents used may be, for example, water, alcohols, such as, forexample, methanol, ethanol or propanol, or mixtures of two or morethereof as known to a skilled person in the art.

The drying temperatures here are preferably in the range of from roomtemperature to 200° C., more preferably of from 60 to 180° C., morepreferably of from 80 to 160° C. and more preferably in the range offrom 100 to 150° C. The durations of drying are preferably in the rangeof from 2 to 48 h, more preferably of from 4 to 36 h.

Moreover, the present invention also relates to the process as describedabove, additionally comprising

-   (iii) separating the zeolitic material from the suspension obtained    according to (ii);-   (iv) drying the zeolitic material, separated according to (iii), at    a temperature in the range of from 100 to 150° C.

According to a particularly preferred embodiment of the processaccording to the invention, the zeolitic material obtained according to(iii) or (iv), preferably after (iv), is calcined in at least oneadditional step.

Therefore, the present invention also relates to above-describedprocess, additionally comprising (v) calcining the zeolitic material.

It is possible in principle to feed the suspension comprising thezeolitic material directly to the calcination. Preferably, the zeoliticmaterial is separated from the suspension, as described above, accordingto (iii), before the calcination. Even more preferably, the zeoliticmaterial is dried before the calcination. The calcination conditions areknown to a person skilled in the art.

Accordingly, the present invention also relates to above-describedprocess, additionally comprising

-   (iii) separating the zeolitic material from the suspension obtained    according to (ii);-   (iv) drying the zeolitic material, separated according to (iii),    preferably at a temperature in the range of from 100 to 150° C.;-   (v) calcining the zeolitic material, dried according to (iv),    preferably at a temperature in the range of from 300 to 750° C.

The present invention also relates to the zeolitic material havingframework structure CHA, obtainable or obtained by above-describedprocess.

The present invention also relates to a zeolitic material/as such,having framework structure CHA, having a composition comprising themolar ratio

(nSiO₂):X₂O₃

wherein X is a trivalent element, and n is at least 10, preferably atleast 15, and wherein the crystal size, as determined from ScanningElectron Microscopy, is greater than 1 micrometer and wherein thechabazite framework is phase-pure having an impurity of other zeoliticframeworks, such as RUT, of less than 5%.

In this context, the term “zeolitic material as such, having frameworkstructure CHA” relates to the calcined zeolitic material which isessentially free of water and from which the structure directing agentand any other organic compounds such as organic acids have beenessentially removed by calcination.

Preferably, n is in the range of from 15 to 70, more preferably in therange of from 15 to 60, more preferably in the range of from 15 to 50.By way of example, especially preferred values of n are 15, 20, 25, 30,40, 45, 50.

Preferably, the trivalent element X is selected from the groupconsisting of Al, B, G, and a mixture of two or more thereof. Accordingto an especially preferred embodiment of the present invention, thetrivalent element X is Al, and even more preferably, Al is the onlytrivalent element building up the CHA zeolitic framework structure.

Even more preferably, the calcined zeolitic material described above isfree of alkali and/or earth alkali metals, in particular free of sodium.The term “free of alkali metal” and “free of sodium”, as used in thiscontext of the present invention relates to zeolitic materials having analkali metal content, and a sodium content, respectively, of 1000 ppm orless, preferably 500 ppm or less, more preferably 300 ppm or less.

According to one embodiment of the present invention, the edges of atleast 90%, preferably at least 95% of the crystallites of the calcinedzeolitic material as described above or of the calcined zeoliticmaterial obtainable or obtained according to the process as describedabove have a mean length in the range of from 1 to 10 microns, morepreferred in the range from 1 to 5 microns, even more preferred in therange from 1 to 2 micrometer, determined via SEM.

According to a preferred embodiment of the present invention, thechabazite framework is phase-pure having an impurity of other zeoliticframeworks, such as RUT, of preferably less than 5%, even more preferredless than 2%, even more preferred less than 1%.

According to a preferred embodiment of the present invention, thecalcined zeolitic material, obtainable or obtained by the process of thepresent invention, or the zeolitic material as such, having CHAframework structure, has a TOC content of 0.1 wt.-% or less, based onthe total weight of the zeolitic material.

According to a preferred embodiment of the present invention, thecalcined zeolitic material, obtainable or obtained by the process of thepresent invention, or the zeolitic material as such, having CHAframework structure, has a BET surface, determined according to DIN66131, in the range of from 300 to 700 m²/g, preferably of from 400 to700 m²/g.

According to a preferred embodiment of the present invention, thecalcined zeolitic material, obtainable or obtained by the process of thepresent invention, or the zeolitic material as such, having CHAframework structure, has a Langmuir surface, determined according to DIN66135, in the range of from 400 to 975 m²/g, preferably of from 550 to975 m²/g.

The zeolitic material according to the present invention may be providedin the form of a powder or a sprayed material obtained fromabove-described separation techniques, e.g. decantation, filtration,centrifugation, or spraying.

In many industrial applications, it is often desired on the part of theuser to employ not the zeolitic material as powder or sprayed material,i.e. the zeolitic material obtained by the separation of the materialfrom its mother liquor, optionally including washing and drying, andsubsequent calcination, but a zeolitic material which is furtherprocessed to give moldings. Such moldings are required particularly inmany industrial processes, e.g. in many processes wherein the zeoliticmaterial of the present invention is employed as catalyst or adsorbent.Such moldings are generally known to a person skilled in the art.

Accordingly, the present invention also relates to a molding comprisingthe zeolitic material having framework structure CHA of the presentinvention.

In general, the zeolitic material described above can be used asmolecular sieve, adsorbent, catalyst, catalyst support or binderthereof. Especially preferred is the use as catalyst. For example, thezeolitic material can be used as molecular sieve to dry gases orliquids, for selective molecular separation, e.g. for the separationand/or storage of hydrocarbons or amides; as ion exchanger; as chemicalcarrier; as adsorbent, in particular as adsorbent for the separation ofhydrocarbons or amides; or as catalyst. Most preferably, the zeoliticmaterial according to the present invention is used as catalyst.

Therefore, the present invention also relates to a catalyst, preferablya molded catalyst, containing the zeolitic material having CHA frameworkstructure as described above. Moreover, the present invention relates tothe use of the zeolitic material having CHA framework structure asdescribed above as a catalyst.

Moreover, the present invention relates to a method of catalyzing achemical reaction wherein the zeolitic material having CHA frameworkstructure according to the present invention is employed ascatalytically active material.

Among others, said catalyst may be employed as catalyst for theselective reduction (SCR) of nitrogen oxides NO_(x); for the oxidationof NH₃, in particular for the oxidation of NH₃ slip in diesel systems;for the decomposition of N₂O; for soot oxidation; for emission controlin Advanced Emission Systems such as Homogeneous Charge CompressionIgnition (HCCl) engines; as additive in fluid catalytic cracking (FCC)processes; as catalyst in organic conversion reactions; as catalyst inthe production of light olefins from a feedstock comprising an oxygenateor mixtures of oxygenates, such as the methanol to olefin reaction; ascatalyst in “stationary source” processes; or as catalyst in methanol toolefins.

Most preferably, the zeolitic material according to the presentinvention or the zeolitic material obtainable of obtained according tothe present invention is used as catalyst, preferably as moldedcatalyst, still more preferably as a molded catalyst wherein thezeolitic material is deposited on a suitable refractory carrier, stillmore preferably on a “honeycomb” carrier, for the selective reduction ofnitrogen oxides NO_(x), i.e. for SCR (selective catalytic reduction) ofnitrogen oxides. In particular, the selective reduction of nitrogenoxides wherein the zeolitic material according to the present inventionis employed as catalytically active material is carried out in thepresence ammonia or urea. While ammonia is the reducing agent of choicefor stationary power plants, urea is the reducing agent of choice formobile SCR systems. Typically, the SCR system is integrated in theengine and vehicle design and, also typically, contains the followingmain components: SCR catalyst containing the zeolitic material accordingto the present invention; a urea storage tank; a urea pump; a ureadosing system; a urea injector/nozzle; and a respective control unit.

Therefore, the present invention also relates to a method forselectively reducing nitrogen oxides NO_(x), wherein a gaseous streamcontaining nitrogen oxides NO_(x), preferably also containing ammoniaand/urea, is contacted with the zeolitic material according to thepresent invention or the zeolitic material obtainable of obtainedaccording to the present invention, preferably in the form of a moldedcatalyst, still more preferably as a molded catalyst wherein thezeolitic material is deposited on a suitable refractory carrier, stillmore preferably on a “honeycomb” carrier.

The term nitrogen oxides, NO_(x), as used in the context of the presentinvention designates the oxides of nitrogen, especially dinitrogen oxide(N₂O), nitrogen monoxide (NO), dinitrogen trioxide (N₂O₃), nitrogendioxide (NO₂), dinitrogen tetroxide (N₂O₄), dinitrogen pentoxide (N₂O₅),nitrogen peroxide (NO₃).

The nitrogen oxides which are reduced using a catalyst containing thezeolitic material according to the present invention or the zeoliticmaterial obtainable of obtained according to the present invention maybe obtained by any process, e.g. as a waste gas stream. Among others,waste gas streams as obtained in processes for producing adipic acid,nitric acid, hydroxylamine derivatives, caprolactame, glyoxal,methylglyoxal, glyoxylic acid or in processes for burning nitrogeneousmaterials may be mentioned.

Especially preferred is the use of a catalyst containing the zeoliticmaterial according to the present invention or the zeolitic materialobtainable or obtained according to the present invention for removal ofnitrogen oxides NO_(x) from exhaust gases of internal combustionengines, in particular diesel engines, which operate at combustionconditions with air in excess of that required for stoichiometriccombustion, i.e., lean.

Therefore, the present invention also relates to a method for removingnitrogen oxides NO_(x) from exhaust gases of internal combustionengines, in particular diesel engines, which operate at combustionconditions with air in excess of that required for stoichiometriccombustion, i.e., at lean conditions, wherein a catalyst containing thezeolitic material according to the present invention or the zeoliticmaterial obtainable or obtained according to the present invention isemployed as catalytically active material.

The following examples shall further illustrate the process and thematerials of the present invention.

EXAMPLES Example 1 Production of an Alkali Metal (Na) Free Chabazite andits Use in Catalysis 1.1 Preparation of the Synthesis Gel

The following starting materials were employed:

-   -   Trimethyl-1-adamantylammonium hydroxide (TMAA, 13.26 wt.-% in        water)    -   Tetramethylammonium hydroxide (TMAOH, 25 wt.-% in water        (Aldrich, Lot 1368537))    -   Aluminum triisopropylate (Aldrich 217557)    -   Ludox AS40 (Grace Davison)

In a 5 liter beaker, 729.7 g of TMAA and 231.1 g of TMAOH solution weremixed. This solution was stirred for 10 min at room temperature. Then,86.6 g of Aluminum triisopropylate were added, and the resultingsuspension was stirred for about 60 min. Subsequently, 952.6 g of LudoxAS40 were added, and the resulting suspension was stirred for about 20min.

The pH of the obtained suspension was measured as 14.2 where the OH/Siwas 0.172.

The suspension had a composition with the following molar ratios: 36SiO₂:2.4 Al isprop.:2.6 TMAA:3.6 TMAOH:434 H₂O. This gel was transferredin to a 2.5 liter autoclave.

1.2 Hydrothermal Crystallization

The autoclave was sealed and heated to a temperature of 170° C. Thetemperature of 170° C. was maintained for 48 h. Thereby, the mixture ina 2.5 L autoclave was stirred at 200 rpm (revolutions/minute).

1.3 Separation, Drying, and Calcination

After the hydrothermal crystallization, the resulting suspension had apH of 12.6. This suspension was admixed (1:1) with deionized water, andthe pH of the resulting suspension was adjusted to 6 with 5% HNO₃. Then,the suspension was filtrated with a porcelain suction filter with adiameter if 15 cm. The wet product was heated to a temperature of 120°C. in air within 30 min and dried at 120° C. for 240 min. The driedproduct was then heated to a temperature of 600° C. within 240 min andcalcined in air at 600° C. for 300 min. The yield was 403 g. A sample ofthe calcined material was examined via XRD, and it was found that azeolite having CHA framework had been obtained (see FIG. 1).

1.4 Characterization of the Product

Elementary analysis of calcined material obtained according to 1.3showed less than 0.1 wt % of C, and less than 0.5 wt % of N. The Nacontent was 0.09 wt % Na₂O reported on a volatile free basis. TheSiO₂:Al₂O₃ was 30:1

The BET surface of the calcined material was 505 m²/g, determinedaccording to DIN 66131, and the Langmuir surface area was 677 m²/g,determined according to DIN 66135. Typical crystallites had a meanlength of about 1-2 micrometers (see FIGS. 2-4).

Example 2 Preparation of Cu Chabazite catalyst for SCR

A Cu containing catalyst was prepared by ion-exchange with copperacetate. A 0.3 M copper (11) acetate monohydrate solution was preparedby dissolving 96 g of the copper salt in 1.6 L of deionized water at 60°C. 300 g of the calcined zeolite of example 1 was then added to thissolution. An ion-exchange reaction between the H-form of the calcinedzeolite described in example 1 and the copper ions was carried out byagitating the slurry at 60° C. for 1 hour. The pH was between 4.5 and4.8 during the reaction. The resulting mixture was then filtered, washeduntil the filtrate had a conductivity of <200 μScm⁻¹, which indicatedthat substantially no soluble or free copper remained in the sample, andthe washed sample was dried at 90° C. The obtained Cu catalyst comprisedCuO at 3.29% by weight and Na at 300 ppm, both reported on a volatilefree basis. The BET surface of the calcined material was 468 m²/g,determined according to DIN 66131, and the Langmuir surface area was 636m²/g, determined according to DIN 66135.

Example 3 SCR Test of Sample from Example 2 3.1 Preparation of a Slurry

150 g of the spray-dried and calcined zeolitic material containing Cuand having CHA framework structure, obtained according to example 6 wasmixed with 358 ml of deionized water. The mixture was ball-milled for 11hours to obtain a slurry which comprised 90% particles smaller than 10micrometer. 26 g of zirconium acetate in dilute acetic acid (containing30% ZrO₂) were added to the slurry with agitation.

3.2 Coating

The slurry was coated onto 1″D×3″ L cellular ceramic cores having a celldensity of 65 cpsc (cells per square cm) (400 cpsi (cells per squareinch)) and a wall thickness of 6.5 mm. The coated cores were dried at110° C. for 3 hours and calcined at 400° C. for 1 hour. The coatingprocess was repeated to obtain a target washcoat loading of 0.146 g/cm³(2.4 g/in³). The washcoat loading is defined as the dry weight gain onthe honeycomb with respect to volume.

3.3 Measuring NOx Selective Catalytic Reduction (SCR) Efficiency

Nitrogen oxides selective catalytic reduction (SCR) efficiency andselectivity of a fresh catalyst core were measured by adding a feed gasmixture of 500 ppm of NO, 500 ppm of NH₃, 10% O₂, 5% H₂O, balanced withN₂ to a steady state reactor containing a 1″D×3″ L catalyst core.

For the catalytic test, the washcoated core was shaped into a squarecross section wrapped with a ceramic insulation mat and placed inside anInconel reactor tube heated by an electrical furnace. The gases, O₂(from air), N₂ and H₂O were preheated in a preheater furnace beforeentering the reactor. The reactive gases NO and NH₃ were introducedbetween the preheater furnace and the reactor.

The reaction was carried at a space velocity of 80,000 h⁻¹ across a 150°C. to 460° C. temperature range. Space velocity is defined as the gasflow rate comprising the entire reaction mixture divided by thegeometric volume of the catalyst core. These conditions define thestandard test for fresh catalysts.

FIG. 5 shows the results of the SCR test, indicating the catalyticefficiency and selectivity of the fresh catalyst. There is a desire toprovide materials that exhibit high performance over a wide temperaturerange, particularly with improvement of low temperature performance.Performance includes NOx conversion but, also selectivity of the SCR toN2 reflected by minimizing the formation of N2O. It can be seen thatthis catalysts exhibits high NOx conversion across the entiretemperature window together with low N2O make (<10 ppm N2O). Theseperformance characteristics are comparable to those of the traditionalmultistep product described in comparative example 3.

3.4 Measuring Hydrothermal Stability of the Catalyst

Hydrothermal stability of the catalyst was measured by hydrothermalaging of the fresh catalyst core (described above under section 3.2) inthe presence of 10 wt.-% H₂O at 850° C. for 6 hours, followed bymeasurement of the nitrogen oxides SCR efficiency and selectivity by thesame process, as outlined above under section 3.3, for the SCRevaluation on a fresh catalyst core.

The results of the SCR efficiency and selectivity of the aged catalystis depicted in FIG. 6. There is a desire to improve hydrothermaldurability over existing zeolitic materials, for example, catalystmaterials which are stable at temperatures up to at least about 650° C.and higher, for example in the range of about 700° C. to about 900° C.It can be seen that this catalyst maintains high NOx conversion over theentire temperature window whilst maintaining high selectivity towardsnitrogen which is reflected in the low N2O make (<20 ppm N2O). Theresults are comparable to the multi-step product described incomparative example 3.

Example 4 Production of an Alkali Metal (Na) Free Chabazite UsingAerosil as the Silica Source 4.1 Preparation of the Synthesis Gel

The following starting materials were employed:

-   -   Trimethyl-1-adamantylammonium hydroxide (TMAA, 13.26 wt.-% in        water)    -   Tetramethylammonium hydroxide (TMAOH, 25 wt.-% in water,        Aldrich)    -   Aluminum triisopropylate (Aldrich 217557)    -   Aerosil 200 (Degussa)

In a 5 liter beaker, 426.8 g of TMAA, 135.1 g of TMAOH solution and1164.7 g deionized water were mixed. This solution was stirred for 10min at room temperature. Then, 50.6 g of Aluminum triisopropylate wereadded, and the resulting suspension was stirred for about 60 min.Subsequently, 222.7 g of Aerosil Silica were added, and the resultingsuspension was stirred for about 20 min.

The pH of the obtained suspension was measured as 12.5 where the OH/Siwas 0.172.

The suspension had a composition with the following molar ratios: 36SiO₂:2.4 Al isprop.: 2.6 TMAA:3.6 TMAOH:881 H₂O. This gel wastransferred in to a 2.5 liter autoclave.

4.2 Hydrothermal Crystallization

The autoclave was sealed and heated to a temperature of 170° C. Thetemperature of 170° C. was maintained for 48 h. Thereby, the mixture ina 2.5 L autoclave was stirred at 200 rpm (revolutions/minute).

4.3 Separation, Drying, and Calcination

After the hydrothermal crystallization, the resulting suspension had apH of 10.5. This suspension was admixed (1:1) with deionized water, andthe pH of the resulting suspension was adjusted to 6 with 5% HNO₃. Then,the suspension was filtrated with a porcelain suction filter with adiameter if 15 cm. The wet product was heated to a temperature of 120°C. in air within 30 min and dried at 120° C. for 240 min. The driedproduct was then heated to a temperature of 600° C. within 240 min andcalcined in air at 600° C. for 300 min. The yield was 224 g. A sample ofthe calcined material was examined via XRD, and it was found that azeolite having CHA framework had been obtained (see FIG. 7).

4.4 Characterization of the Product

Elementary analysis of calcined material obtained according to 1.3showed less than 0.1 wt % of C, and less than 0.5 wt % of N. The Nacontent was 0.03 wt % Na₂O reported on a volatile free basis. TheSiO2:Al2O3 was 28:1

The BET surface of the calcined material was 493 m²/g, determinedaccording to DIN 66131, and the Langmuir surface area was 660 m²/g,determined according to DIN 66135. Typical crystallites had a meanlength of about 2 to 4 micrometers (see FIGS. 8-10).

Comparative Example 1 Production of Na Chabazite and its Use inCatalysis 1.1 Preparation of the Synthesis Gel

The following starting materials were employed:

-   -   Trimethyl-1-adamantylammonium hydroxide (TMAA, 13.26 wt.-% in        water)    -   sodium hydroxide (>98% NaOH (anhydrous pellets), Aldrich)    -   Aluminum triisopropylate (Aldrich 217557)    -   Ludox AS40 (Grace Davison)

In a 5 liter beaker, 894.7 g of TMAA and 31.2 g of NaOH solution weremixed. This solution was stirred for 10 min at room temperature. Then,106.2 g of Aluminum triisopropylate were added, and the resultingsuspension was stirred for about 60 min. Subsequently, 1168 g of LudoxAS40 were added, and the resulting suspension was stirred for about 20min.

The pH of the obtained suspension was measured as 13.7 where the OH/Siwas 0.172.

The suspension had a composition with the following molar ratios: 36SiO₂:2.4 Al isprop.: 2.6 TMAA:3.6 NaOH:379 H₂O. This gel was transferredin to a 2.5 liter autoclave.

1.2 Hydrothermal Crystallization

The autoclave was sealed and heated to a temperature of 170° C. Thetemperature of 170° C. was maintained for 40 h. Thereby, the mixture ina 2.5 L autoclave was stirred at 200 rpm (revolutions/minute).

1.3 Separation, Drying, and Calcination

After the hydrothermal crystallization, the resulting suspension had apH of 11.9. This suspension was admixed (1:1) with deionized water, andthe pH of the resulting suspension was adjusted to 7 with 5% HNO₃. Then,the suspension was filtrated with a porcelain suction filter with adiameter if 15 cm. The wet product was heated to a temperature of 120°C. in air within 30 min and dried at 120° C. for 240 min. The driedproduct was then heated to a temperature of 600° C. within 240 min andcalcined in air at 600° C. for 300 min. The yield was 420 g. A sample ofthe calcined material was examined via XRD, and it was found that azeolite having CHA framework had been obtained (see FIG. 11).

1.4 Characterization of the Product

Elementary analysis of calcined material obtained according to 1.3showed less than 0.1 wt % of C, and less than 0.5 wt % of N. The Nacontent was 0.7 wt % Na₂O reported on a volatile free basis. TheSiO₂:Al₂O₃ was 30:1

The BET surface of the calcined material was 592 m²/g, determinedaccording to DIN 66131, and the Langmuir surface area was 803 m²/g,determined according to DIN 66135. Typical crystallites had a meanlength of about 73 nanometers as determined by xrd but, also shown inthe SEM images (see FIGS. 12-14).

Comparative Example 2 Preparation of NH4 form then Cu Chabazite Catalystfor SCR 2.1 Ammonium Exchange

An ammonium exchange was carried out to reduce the Na content of thematerial. The NH₄-form of the zeolite was prepared by ion-exchange withammonium nitrate. 40 g of ammonium nitrate was dissolved in 4000 g ofdeionized water with mixing. This solution was heated to 60° C. Then 400g of calcined Na-zeolite as described in comparative example 1.4 wasadded to the solution. An ammonium exchange was carried out at 60° C.for 1 hour. The resulting mixture was then filtered, washed until thefiltrate had a conductivity of <200 μScm⁻¹, which indicated thatsubstantially no soluble or free ions remained in the sample, and thewashed sample was dried at 90° C. The obtained NH₄-form zeolitecomprised NH₄ at 0.62% by weight and Na₂O at less than 100 ppm.

2.3 Copper Exchange

A Cu containing catalyst was prepared by ion-exchange with copperacetate. A copper (II) acetate monohydrate solution was prepared bydissolving 47.9 g of the copper salt in 800 L of deionized water at 60°C. 200 g of the NH4-form described in comparative example 2.1 was thenadded to this solution. An ion-exchange reaction between the NH₄-form ofthe zeolite described in comparative example 2.1 and the copper ions wascarried out by agitating the slurry at 60° C. for 1 hour. The pH wasbetween 5 and 5.3 during the reaction. The resulting mixture was thenfiltered, washed until the filtrate had a conductivity of <200 μScm⁻¹,which indicated that substantially no soluble or free copper remained inthe sample, and the washed sample was dried at 90° C. The obtained Cucatalyst comprised CuO at 3.4% by weight and Na₂O at less than 100 ppm.The SiO₂:Al₂O₃ was 29.

Comparative Example 3 SCR Test of Sample from Comparative Example 2 3.1Preparation of a Slurry

150 g of the spray-dried and calcined zeolitic material containing Cuand having CHA framework structure, obtained according to comparativeexample 2.3 was mixed with 358 ml of deionized water. The mixture wasball-milled for 11 hours to obtain a slurry which comprised 90%particles smaller than 10 micrometer. 26 g of zirconium acetate indilute acetic acid (containing 30% ZrO₂) were added to the slurry withagitation.

3.2 Coating

The slurry was coated onto 1″D×3″ L cellular ceramic cores having a celldensity of 65 cpsc (cells per square cm) (400 cpsi (cells per squareinch)) and a wall thickness of 6.5 mm. The coated cores were dried at110° C. for 3 hours and calcined at 400° C. for 1 hour. The coatingprocess was repeated to obtain a target washcoat loading of 0.146 g/cm³(2.4 g/in³). The washcoat loading is defined as the dry weight gain onthe honeycomb with respect to volume.

3.3 Measuring NOx Selective Catalytic Reduction (SCR) Efficiency

Nitrogen oxides selective catalytic reduction (SCR) efficiency andselectivity of a fresh catalyst core were measured by adding a feed gasmixture of 500 ppm of NO, 500 ppm of NH₃, 10% O₂, 5% H₂O, balanced withN₂ to a steady state reactor containing a 1″D×3″ L catalyst core.

For the catalytic test, the washcoated core was shaped into a squarecross section wrapped with a ceramic insulation mat and placed inside anInconel reactor tube heated by an electrical furnace. The gases, O₂(from air), N₂ and H₂O were preheated in a preheater furnace beforeentering the reactor. The reactive gases NO and NH₃ were introducedbetween the preheater furnace and the reactor.

The reaction was carried at a space velocity of 80,000 h⁻¹ across a 200°C. to 460° C. temperature range. Space velocity is defined as the gasflow rate comprising the entire reaction mixture divided by thegeometric volume of the catalyst core. These conditions define thestandard test for fresh catalysts.

FIG. 15 shows the results of the SCR test, indicating the catalyticefficiency and selectivity of the fresh catalyst. There is a desire toprovide materials that exhibit high performance over a wide temperaturerange, particularly with improvement of low temperature performance.Performance includes NOx conversion but, also selectivity of the SCR toN2 reflected by minimizing the formation of N2O. It can be seen thatthis catalysts exhibits high NOx conversion across the entiretemperature window together with low N2O make (<10 ppm N2O).

3.4 Measuring Hydrothermal Stability of the Catalyst

Hydrothermal stability of the catalyst was measured by hydrothermalaging of the fresh catalyst core (described above under section 3.2 ofthe comparative examples) in the presence of 10 wt.-% H₂O at 850° C. for6 hours, followed by measurement of the nitrogen oxides SCR efficiencyand selectivity by the same process, as outlined above under section 3.3of the comparative examples, for the SCR evaluation on a fresh catalystcore.

The results of the SCR efficiency and selectivity of the aged catalystis depicted in FIG. 16. There is a desire to improve hydrothermaldurability over existing zeolitic materials, for example, catalystmaterials which are stable at temperatures up to at least about 650° C.and higher, for example in the range of about 700° C. to about 900° C.It can be seen that this catalyst maintains high NOx conversion over theentire temperature window whilst maintaining high selectivity towardsnitrogen which is reflected in the low N₂O make (<20 ppm N₂O).

Comparative Example 4 Production of an Alkali Metal Free Chabazite UsingIncreased Amounts of Trimethyladamantyl Ammonium Hydroxide 4.1Preparation of the Synthesis Gel

The following starting materials were employed:

-   -   Trimethyl-1-adamantylammonium hydroxide (TMAA, 20.17 wt.-% in        water)    -   Aluminum triisopropylate (Aldrich 217557)    -   Ludox AS40 (Grace Davison)

In a 5 liter beaker, 1048.2 g of TMAA were mixed. This solution wasstirred for 10 min at room temperature. Then, 79.3 g of Aluminumtriisopropylate were added, and the resulting suspension was stirred forabout 60 min. Subsequently, 872.5 g of Ludox AS40 were added, and theresulting suspension was stirred for about 20 min.

The pH of the obtained suspension was measured as 13.5 where the OH/Siwas 0.172.

The suspension had a composition with the following molar ratios: 36SiO₂:2.4 Al isprop.: 6.2 TMAA:468 H₂O. This gel was transferred in to a2.5 liter autoclave.

4.2 Hydrothermal Crystallization

The autoclave was sealed and heated to a temperature of 170° C. Thetemperature of 170° C. was maintained for 48 h. Thereby, the mixture ina 2.5 L autoclave was stirred at 200 rpm (revolutions/minute).

4.3 Separation, Drying, and Calcination

After the hydrothermal crystallization, the resulting suspension had apH of 12.4. This suspension was admixed (1:1) with deionized water, andthe pH of the resulting suspension was adjusted to 6 with 5% HNO₃. Then,the suspension was filtrated with a porcelain suction filter with adiameter if 15 cm. The wet product was heated to a temperature of 120°C. in air within 30 min and dried at 120° C. for 240 min. The driedproduct was then heated to a temperature of 600° C. within 240 min andcalcined in air at 600° C. for 300 min. The yield was ˜368 g. A sampleof the calcined material was examined via XRD, and it was found that azeolite having CHA framework had been obtained (see FIG. 17).

4.4 Characterization of the Product

Elementary analysis of calcined material obtained according to 1.3showed less than 0.1 wt % of C, and less than 0.5 wt % of N. The Nacontent was 0.17 wt % Na₂O reported on a volatile free basis. The higherNa content is attributed to Na from the TMAA solution. The SiO₂:Al₂O₃was 30:1

The BET surface of the calcined material was 711 m²/g, determinedaccording to DIN 66131, and the Langmuir surface area was 960 m²/g,determined according to DIN 66135. SEM images of the product indicatethat the product has agglomerates of ˜1 micron. Where the primaryparticle size has typical crystallites with a mean length of less thanabout 80 nanometers (see FIG. 18). This was confirmed by measurement byxrd.

The invention is advantageous as it avoids ion-exchange steps normallyneeded to attain a catalytic composition of low-alkali metal content.Additionally the process provides a time and cost saving process for thepreparation of zeolitic materials having CHA framework structure andavoids the additional complexity of ion-exchange steps. The ion-exchangesteps can lead to instability in the zeolitic materials throughprocesses such as dealumination. The larger crystals formed by theinventive process could offer improved stability.

SHORT DESCRIPTION OF THE FIGURES

FIG. 1 shows the XRD pattern of the calcined zeolitic material havingCHA framework type according to Example 1. The powder X-ray diffractionpatterns were recorded on a Siemens D-5000 with monochromatic Cu Kalpha-1 radiation, a capillary sample holder being used in order toavoid preferred orientation. The diffraction data were collected using aposition-sensitive detector from Braun, in the range from 8 to 96° (2theta) and with a step width of 0.0678°. Indexing of the powder patternwas effected using Treor90, implemented in powder-X (Treor90 is a publicdomain program which is freely accessible via the URLhttp://www.ch.iucr.org/sincris-top/logiciel/). In the figure, the angle2 theta in ° is shown along the abscissa and the intensities (LC=Linecounts) are plotted along the ordinate.

FIG. 2 shows crystallites of the calcined zeolitic material having CHAframework

type according to Example 1, determined by SEM (Fig. with secondaryelectrons 5 kV; scale: 1000:1).

FIG. 3 shows crystallites of the calcined zeolitic material having CHAframework type according to Example 1, determined by SEM (Fig. withsecondary electrons 5 kV; scale: 5000:1).

FIG. 4 shows crystallites of the calcined zeolitic material having CHAframework type according to Example 1, determined by SEM (Fig. withsecondary electrons 5 kV; scale: 20000:1).

FIG. 5 shows the result of an SCR test of the material obtainedaccording to example 2 applied onto a cellular ceramic core according toexample 3 (fresh SCR). Abbreviation “%” for the conversion of NOx, andNH₃. Abbreviation “ppm” for N₂O make. The symbols of the curvesrepresent the following chemical compounds:

♦ NOx (conversion) ▪ NH₃ (conversion) ▴ N₂O (production)

FIG. 6 shows the result of an SCR test of the material obtainedaccording to example 2 applied onto a cellular ceramic core according toexample 2 (aged SCR). Abbreviation “%” for the conversion of NOx, andNH₃. Abbreviation “ppm” for N₂O make. The symbols of the curvesrepresent the following chemical compounds

♦ NOx (conversion) ▪ NH₃ (conversion) ▴ N₂O (production)

FIG. 7 shows the XRD pattern of the calcined zeolitic material havingCHA framework type according to example 4. As to the method ofdetermining the XRD pattern, see FIG. 1.

FIG. 8 shows crystallites of the calcined zeolitic material having CHAframework type according to example 4, determined by SEM (Fig. withsecondary electrons 5 kV; scale: 5000:1).

FIG. 9 shows crystallites of the calcined zeolitic material having CHAframework type according to comparative example 4, determined by SEM(Fig. with secondary electrons 5 kV; scale: 20000:1).

FIG. 10 shows crystallites of the calcined zeolitic material having CHAframework type according to comparative example 4, determined by SEM(Fig. with secondary electrons 5 kV; scale: 50000:1).

FIG. 11 shows the XRD pattern of the Cu containing calcined zeoliticmaterial having CHA framework type according to comparative example 1.As to the method of determining the XRD pattern, see FIG. 1.

FIG. 12 shows crystallites of the calcined zeolitic material having CHAframework type according to comparative example 1, determined by SEM(Fig. with secondary electrons 5 kV; scale: 5000:1).

FIG. 13 shows crystallites of the calcined zeolitic material having CHAframework type according to comparative example 1, determined by SEM(Fig. with secondary electrons 5 kV; scale: 20000:1).

FIG. 14 shows crystallites of the calcined zeolitic material having CHAframework type according to comparative example 1, determined by SEM(Fig. with secondary electrons 5 kV; scale: 50000:1)

FIG. 15 shows the result of an SCR test of the material obtainedaccording to comparative example 2 applied onto a cellular ceramic coreaccording to comparative example 3 (fresh SCR). Abbreviation “%” for theconversion of NOx, and NH₃. Abbreviation “ppm” for N₂O make. The symbolsof the curves represent the following chemical compounds:

♦ NOx (conversion) ▪ NH₃ (conversion) ▴ N₂O (production)

FIG. 16 shows the result of an SCR test of the material obtainedaccording to comparative example 2 applied onto a cellular ceramic coreaccording to comparative example 3 (aged SCR). Abbreviation “%” for theconversion of NOx, and NH₃. Abbreviation “ppm” for N₂O make. The symbolsof the curves represent the following chemical compounds

♦ NOx (conversion) ▪ NH₃ (conversion) ▴ N₂O (production)

FIG. 17 shows the XRD pattern of the calcined zeolitic material havingCHA framework type according to comparative example 4. As to the methodof determining the XRD pattern, see FIG. 1.

FIG. 18 shows crystallites of the calcined zeolitic material having CHAframework type according to comparative example 4, determined by SEM(Fig. with secondary electrons 5 kV; scale: 50000:1).

1. A process for the preparation of zeolites having CHA framework structure and a composition comprising the molar ratio (n SiO₂):X₂O₃, wherein X is a trivalent element, and wherein n is at least 10, the process comprising: (i) preparation of an aqueous solution containing: at least one source for X₂O₃, wherein X is selected from Al, B, Ga, and a mixture of two or more, at least one source for SiO₂, at least one organic structure directing agent (SDA) other than Tetramethylammonium hydroxide (TMAOH) as a template for the CHA structure, and Tetramethylammonium hydroxide (TMAOH), wherein the SDA or mixtures thereof are employed in such amounts that the aqueous solution in (i) exhibits a molar ratio of SDA:TMAOH in the range of 0.01 to 5; (ii) hydrothermal crystallization of the aqueous solution according to (i); wherein the aqueous solution of (i) contains copper in an amount less than 0.005 Cu:((n SiO₂)+X₂O₃) where n is at least
 10. 2. The process of claim 1, wherein X comprises Al.
 3. The process of claim 1, wherein the aqueous solution subjected to hydrothermal crystallization according to (ii) is free of alkali and/or earth alkali metals.
 4. The process of claim 1, wherein the structure directing agent comprises a 1-adamantyltrimethylammonium compound or a mixture of a 1-adamantyltrimethylammonium compound and a benzyltrimethylammonium compound.
 5. The process of claim 1, wherein the pH of the aqueous solution obtained in (i) is in the range of 10 to
 14. 6. The process of claim 1, wherein the ratio of SDA:TMAOH is in the range of 0.7 to
 3. 7. The process of claim 1, wherein the at least one source for SiO₂ and the at least one source for X₂O₃ are employed in such amounts that the aqueous solution obtained according to (i) exhibits a molar ratio of water relative to the sum of (n X₂O₃) and SiO₂, relative to the structure directing agent (SDA), optionally the sum of SDAs, and TMAOH (qH₂O):[(nSiO₂)+X₂O₃]:(sSDA):(tTMAOH) wherein q is at least 10, n is 10 to 1000, s is 0.025 to 0.1 and t is 0.01 to 0.1.
 8. The process of claim 1, wherein the aqueous solution obtained according to (i) has a OH−/Si ratio in the range of 0.1 to 0.5.
 9. The process of claim 1, additionally comprising (iii) separating the zeolitic material from the suspension obtained according to (ii); (iv) drying the zeolitic material, separated according to (iii), at a temperature in the range of from 100 to 150° C.; (v) calcining the zeolitic material, dried according to (iv), at a temperature in the range of from 300 to 750° C.
 10. A zeolitic material having framework structure CHA, obtainable by the process of claim
 1. 11. A zeolitic material having framework structure CHA, having a composition comprising the molar ratio (n SiO₂):X₂O₃, wherein X is a trivalent element, and wherein X is selected from Al, B, Ga, and a mixture of two or more, and n is at least 10, and wherein the crystal size of that zeolitic material, as determined from Scanning Electron Microscopy, is greater than 1 micrometer and wherein the chabazite framework is phase-pure having an impurity of other zeolitic frameworks of less than 5%, as determined by X-ray Diffraction.
 12. The zeolitic material of claim 11, wherein the crystal size is in the range of 1 to 5 microns.
 13. The zeolitic material of claim 11, wherein the chabazite framework is phase-pure having an impurity of other zeolitic frameworks of less than 1%.
 14. A method for the selective reduction (SCR) of nitrogen oxides NO_(x), for the oxidation of NH₃ or for the decomposition of N₂O, the method comprising contacting a stream comprising NOx, NH₃ or N₂O with a catalyst comprising the zeolitic material of claim
 10. 15. A method for catalyzing a chemical reaction, the method comprising using the zeolitic material of claim 10 as a catalytically active material in a chemical reaction.
 16. A catalyst comprising the zeolitic material of claim
 10. 17. A method for the selective reduction (SCR) of nitrogen oxides NO_(x), for the oxidation of NH₃ or for the decomposition of N₂O, the method comprising contacting a stream comprising NOx, NH₃ or N₂O with a catalyst comprising the zeolitic material of claim
 11. 18. A method for catalyzing a chemical reaction, the method comprising using the zeolitic material of claim 11 as a catalytically active material in a chemical reaction.
 19. A catalyst comprising the zeolitic material of claim
 11. 